Ferritic alloy steels for use at elevated temperatures



FERRITIC .ALLOY .STEELSEEOR USE-NI ELEVATED TEMPERATURES Henry'William Kirkby and "Charles sykes, sh arer-(man land, assignors toFirth-VickersStai'lilss SteelsIiimited,

Sheffield,EnglandyaBritish company No Drawing. Application March 11, 1957 Serial No. 645,004

Claims priority, application Great Britain March 29, 1956 Claims. (Cl. 75126) This invention relates to improvements relating to ferritic alloy steels for use at elevated temperatures.

An object of the invention is to provide a forgeable ferritic alloy steel possessing improved creep resistance at temperatures up to 700 C. 1

British specification No. 658,115 (hereinafter referred to as the earlier specification) describes a forgeable ferritic alloy steel having a composition characterised by the absence of nickel above a proportion of 1.5% and by the presence as essential constituents of 0.05-0.5% carbon, 4-20% chromium, 0.5-3% molybdenum and/or tungsten, 0.22.5% niobium, 0.05-0.25% nitrogen, 0.003- 0.5% boron and 0.1-2% vanadium. The alloy may also contain silicon up to 3% manganese up to 4% and cobalt up to The preferred proportions of the various constituents, as described in the earlier specification are:

Percent Alloy steels of the above composition possess stressto-rupture properties of the following order:

At 650 C.: Rupture strength (hrs.) tons/sq. in. 463 17 tons/sq. in. 30

It has now been found that with certain modification in the composition described in the earlier specification substantially higher rupture strength at 650 C. can be obtained. It will be noted that in the earlier composition the maximum range of the tungsten content was 0.5 to 3.0%. According to the principal modification of the present invention an increased amount of tungsten is incorporated, the new range being over 3% and up to 16%.

The alloys of this invention comprise as essential constituents 0.03 to 0.30% carbon, 4% to 20% chromium, over 3 and up to 16% tungsten, 0.1 to 2.0% vanadium, and 0.05 to 2.5% niobium interchangeable wholly or in part by tantalum. The alloys may also contain up to 2.0% silicon, up to 4% manganese, up to 1.5% nickel, up to 0.25% nitrogen, up to 0.5% boron and up to 20% cobalt.

2,880,085 Patented Mar. 31 1959 The preferred proportions of the variousconstituents are as follows:

7 Percent Carbon 4--.... 0103 :to 0.20 '-'Silico'n a 0.3 to 1.5 Manganese -05 to" 1.5 -t0 Chromium 9:0 to 16.0 Tungsten Over 3.0 -up *to 10.0 Vanadium 0.1 to 0.7 Niobium (interchangeable with tantalum) 0.05 to 1.0 Nitrogen Up to 0.10 Boron Up to 0.10 Cobalt 5.0 to 15.0 Iron Remainder Alloy A, Alloy B, Alloy 0, Earlier Specification tons/sq. tons/sq. tons/sq.

in. in. in.

163-1615 tons/sq. in. approx n 20 i 25 I 28 The alloys A, B, C contain respectively 4%, 6% and 8% of tungsten, and it will be noted that, with the particular alloys concerned, the rupture strength is approximately a function of the tungsten content.

As is known, the creepresistance of an alloy steel depends to some extent on the heat treatment to which it has been subjected. The term suitable heat treatment" as used above is intended to convey that the temperature, the rate of heating and cooling, and the duration of the treatment are such that optimum properties are developed for the particular composition. An example of heat treatment suitable in some cases is to harden in air or oil from about 1160 C. followed by a tampering treatment at 675 C.

We claim:

1. A forgeable ferritic alloy steel comprising 0.03 to 0.30% carbon, 4 to 20% chromium, over 3 and up to 16% tungsten, 0.1 to 2.0% vanadium, and 0.05 to 2.5% of at least one element from the group consisting of niobium and tantalum, and the balance iron with incidental impurities in ordinary amounts.

2. A forgeable ferritic alloy steel comprising, 0.03 to 0.30% carbon, 4 to 20% chromium, over 3 and up to 16% tungsten, 0.1 to 2.0% vanadium, up to 2% of silicon, up to 4% of manganese, up to 1.5% of nickel, up to 0.25 nitrogen, up to 0.5% of boron, up to 20% of cobalt, 0.05 to 2.5% of at least one element from the group consisting of niobium and tantalum, and the balance iron with incidental impurities in ordinary amounts.

3. A foregable ferritic alloy steel comprising, 003 to 0.20% carbon, 0.3 to 1.5% silicon, 0.5 to 1.5% manganese, 0.1 to 1.0% nickel, 9 to 16% chromium, over 3 and up to 10% tungsten, 0.1 to 0.7% vanadium, 5 to 15% cobalt, up to 0.10% nitrogen, up to 0.10% boron and 0.05 to 1.0% of at least one element from the group consisting of niobium and tantalum, and the balance iron with incidental impurities in ordinary amounts.

4. A forgeable ferritic alloy steel comprising, 0.03 to 0.30% carbon, 4 to 20% chromium, over 3 and up to 16% tungsten, 0.1 to 2.0% vanadium, up to 2.0% of silicon, up to 4.0% manganese, up to 1.5% of nick l,

.. 3 up to 0.25% of nitrogen, up to 0.5% of boron, up to 20% of cobalt, up to 3% of molybdenum, and 0.05 to 2.5% of at least one element from the group consisting of niobium and tantalum, and the balance iron with incidental impurities in ordinary amounts.

5. A forgeable ferritic alloy steel article characterized by a rupture strength, expressed as stress for 100 hours at 650 C. of the order of 20 to 28 tons per square inch and having a composition consisting essentially of nickel up to about 1.5%, of 0.03 to 0.30% carbon, 4 to 20% chromium, 4 to 8% tungsten, 0.1 to 2.0% vanadium and 0.05 to 2.5% of at least one element selected from the group consisting of niobium and tantalum, and the balance iron with incidental impurities in ordinary amounts.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,385 Mahin Aug. 19, 1941 2,432,614 Franks et a1 Dec. 16, 1947 2,462,665 Olcott Feb. 22, 1949 2,542,220 Urban et a1 Feb. 20, 1951 2,590,835 Kirkby et a1. Apr. 1, 1952 

1. A FORGEABLE FERRITIC ALLOY STEEL COMPRISING 0.03 TO 0.30% CARBON, 4 TO 20% CHROMIUM, OVER 3 AND UP TO 16% TUNGSTEN, 0.1 TO 0.0% VANADIUM AND 0.05 TO 2.5% OF AT LEAST ONE ELEMENT FROM THE GROUP CONSISTING OF NIOBIUM AND TANTALUM, AND THE BALANCE IRON WITH INCIDENTAL IMPURITIES IN ORDINARY AMOUNTS. 